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'''Anaphylatoxins''', or '''anaphylotoxins''', are fragments ([[C3a]], [[C4a]] or [[C5a]]) that are produced during the pathways of the [[complement system]]. 

==Direct and indirect functions==
Most notable is the ability to trigger [[degranulation]] of (release of substances from) [[mast cells]] or [[basophil]]s, which is an important part of the [[immune system]] in all kinds of [[inflammation]] and especially as part of defense against [[parasite]]s. If the degranulation is too strong, it can cause [[allergic reaction]]s.

Anaphylatoxins indirectly mediate:
*spasms of [[smooth muscle|smooth muscle cells]], for example [[bronchospasm]]s
*increase in the permeability of [[capillary|blood capillaries]]
*[[chemotaxis]] &mdash; [[receptor (biochemistry)|receptor]]-mediated movement of [[leukocyte]]s in the direction of the increasing concentration of anaphylatoxins

==Examples==
Important anaphylatoxins:

* C3a is not as strong as C5a, but stronger than C4a and can trigger degranulation of Mast-cells and serve as a chemotactic targeting molecule for eosinophile granulocytes.
* C4a is the least active anaphylatoxin
* C5a is the strongest toxin in the row, it is a very strong mediator of inflammation.
** [[co-stimulation]] of C3b at times of phagocytosis (not possible without C5a).
** Chemotactor and activator for granulocytes in general and macrophages
** stimulates respiratory burst in Neutrophils
** increases vascular permeability
** contracts smooth muscle cells
** activates mastcells to churn out Histamine and TNF-Alpha

==Terminology==
Although some drugs ([[morphine]], [[codeine]], synthetic [[ACTH]]) and some [[neurotransmitter]]s ([[norepinephrine]], [[substance P]]) are important mediators of degranulation of mast cells or basophils, they are generally not called anaphylatoxins. This term is reserved only for fragments of the complement.

== See also ==
*[[Allergy]]
*[[Anaphylaxis]]
*[[Complement system]]
*[[Inflammation]]
*[[Immune system]]
*[[Nervous system]]

==External links==
* {{MeshName|Anaphylatoxin}}
* {{eMedicineDictionary|Anaphylatoxin}}

{{Immune system}}
[[Category:Complement system]]

[[de:Anaphylatoxin]]
[[pt:Anafilatoxina]]
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